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MULTIPLE INPUT MULTIPLE OUTPUT SYSTEMS (MIMO). By MOHAMMED BERHEA. 1. Introduction. MIMO Systems: use multiple inputs and multiple outputs from a single channel are defined by Spatial Diversity and Spatial Multiplexing. Spatial Diversity and Spatial Multiplexing. Spatial Diversity

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1 introduction
1. Introduction

MIMO Systems:

  • use multiple inputs and multiple outputs from a single channel
  • are defined by Spatial Diversity and Spatial Multiplexing
spatial diversity and spatial multiplexing
Spatial Diversity and Spatial Multiplexing
  • Spatial Diversity
    • Signal copies are transferred from multiple antennas or received at more than one antenna
    • redundancy is provided by employing an array of antennas, with a minimum separation of λ/2 between neighbouring antennas
  • Spatial Multiplexing
    • the system is able to carry more than one data stream over one frequency, simultaneously
why mimo
Why MIMO?
  • There is always a need for increase in performance in wireless systems
    • Significant increase in spectral efficiency and data rates
    • High Quality of Service (QoS)
    • Wide coverage, etc.
  • Wireless channel that we are using is very unfriendly
    • Suffers from Co–channel interference and signal level fading
    • It provides a limited bandwidth
    • power falls off with distance
mimo system solutions
MIMO System solutions
  • By using Multiple Output Multiple Input (MIMO) systems
    • Diversity gain mitigates the fading and increases coverage and improves QoS
    • Multiplexing gain increases capacity and spectral efficiency with no additional power or bandwidth expenditure
    • Array gain results in an increase in average receive SNR.
  • Spatial Diversity and Spatial Multiplexing can be conflicting goals
spatial multiplexing
Spatial Multiplexing
  • MIMO channels can be decomposed into a number of R parallel independent channels → Multiplexing Gain
    • Principle: Transmit independent data signals from different antennas to increase the throughput, capacity.

Source: An Overview of MIMO Systems in Wireless Communications

www.iet.ntnu.no/projects/beats/Documents/mimo.pdf

memo capacity on fading channels
MEMO capacity on fading channels
  • The capacity increase can be seen by comparing MEMO systems with SISO, SIMO, and MISO systems
    • SISO:capacity is given by Shannon’s classical formula:

Where B is the BW and h is the fading gain

    • SIMO (with M transmitting antennas), the capacity is given by [2]
    • MISO (with M transmitting antennas), the capacity is given by [2]
memo capacity on fading channels1
MEMO capacity on fading channels
  • The capacity for MIMO systems can have the following forms (Assuming Tx antennas = Rx antennas = N):

A) If the channel is not known at the transmitter:

    • Where Es is the total power, σ2 is noise level of AWGN
    • Hence the power is equally shared by each channel
    • The capacity grows linearly with the number of antennas

B) If the channel is known at the transmitter

memo capacity on fading channels2
MEMO capacity on fading channels
  • With the channel known at the transmitter, the total power allocation the each channel will be based on watterfilling.
    • Watterfilling: Strong Sub-channel, with low noise power level will be assigned with a higher signal power.

Where σN2 = σ2 / │hn2│

Illustrating Watterfilling

Source: MIMO Systems and Transmit Diversity, www.comm.utoronto.ca/~rsadve/Notes/DiversityTransmit.pdf

average capacity of a mimo rayleigh fading channel
Average capacity of a MIMO Rayleigh fading channel []

Source: Space-time Diversity Codes for Fading Channels, [3]

spatial diversity
Spatial Diversity
  • Improves the signal quality and achieves a higher SNR at the receiver-side
  • Principle of diversity relies on the transmission of structured redundancy

yi

xi

mimo diversity and reliability
MIMO Diversity and Reliability
  • The performance improvement in SNR and error probability for MIMO can be compared with SISO, SIMO, and MISO
  • The detailed calculation for SNR and Pe is shown in [1]
    • SISO:
    • Receive Diversity (SIMO):

and

and

mimo diversity and reliability1
MIMO Diversity and Reliability
  • The values for SNR and Pe for:
    • Transmit Diversity (MISO):
    • Transmit/Receive Diversity (MIMO):
      • The received signal at antenna i will be:
      • H is the channel fading matrix

and

and

conclusion
Conclusion
  • The capacity of Receive or Transmit Diversitygrows logarithmically with the number of antennas
  • Capacity of MEMO increases linearly with the number of antennas
  • Using Spatial Diversity:
    • The SNR increases and Pe decreases when using MIMO
  • Spatial Multiplexing and Spatial Diversity are conflicting objectives
references
References

[1] MIMO Architecture for Wireless Communication: Intel Technology Journal, vol. 10, Issue 02, May 2006

[2] MIMO Systems and Transmit Diversity,

www.comm.utoronto.ca/~rsadve/Notes/DiversityTransmit.pdf

[3] R.A. Carrasco, Space-time Diversity Codes for fading Channel,

Staffordshire University

[4] D. Gesbert, M.Shafi, D. Shiu, P. Smith, and A. Naguib, “From Theory to Practice: An Overview of MIMO Space–Time Coded Wireless Systems”

IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 21, NO. 3, APRIL 2003

[5] Introduction to MIMO Systems: Application Note 1MA102, Rohde & schwarz